The present invention relates to a semiconductor device, and a method for producing a semiconductor device, and is a technique applicable to, for example, a power device.
As a switching element for supplying electric power, a power device is frequently used. The power device has, for example, a structure described in Japanese Unexamined Patent Application Publication No. 2010-92895 (Patent Literature 1). In Patent Literature 1, a semiconductor substrate is used to form a vertical transistor. Specifically, the semiconductor substrate has a first surface and a second surface opposite to each other. The transistor has a source in the first surface, and has a drain in the second surface.
Furthermore, according to Patent Literature 1, the source is made of a first electrode formed on the first surface, and the drain is made of a second electrode formed on the second surface. The first and second electrodes are made of a metal, or metals having the same thermal expansion coefficient. Patent Literature 1 states that according to this structure, the semiconductor substrate is prevented from being warped even when heat is applied to the semiconductor substrate.
JP-A No. 2005-244165 (Patent Literature 2) describes the following semiconductor chip: a semiconductor chip having a first surface and a second surface opposite to each other, in which a first electrode is formed on the first face, and a second electrode is formed on the second surface.
According to Patent Literature 2, the semiconductor chip is produced as follows: A first electrode is initially formed on a first surface of a semiconductor wafer. Next, a supporting substrate which is to face the semiconductor wafer is located over the first surface of the semiconductor wafer to interpose the first electrode between the substrate and the wafer. Next, a second electrode is formed on a second surface of the semiconductor wafer. Next, the supporting substrate is taken away from the semiconductor wafer. Next, the semiconductor wafer is diced. In this way, the above-mentioned semiconductor chip is obtained. Patent Literature 2 states that even when the first and second electrodes are located over the first and second surfaces, respectively, the semiconductor wafer can be restrained from being warped by effect of the supporting substrate.
As a substrate in which transistors are formed, a silicon substrate is frequently used. However, the silicon substrate may be warped by, for example, an interconnection layer (insulating layer) formed on a surface of the silicon substrate. This warp may cause the silicon substrate to be cracked. The inventors have made investigations for restraining a silicon substrate from being warped. Other objects and novel features of the present invention will be made evident from the description of the present specification, and attached drawing.